Robustness of model reference adaptive control systems with magnified leakage term

This paper investigates the robustness of model reference adaptive control (MRAC) of a class of uncertain dynamical system using state information. The controller structure used is standard in the literature of adaptive control, and the parameter update law adopted incorporates some magnified leakage term, such as the well-known σ-modification. But unlike the MRAC of system with only I/O measurement, the scheme presented can be robust, with arbitrarily high level of matched uncertainties. It is also shown that such scheme differs from those proposed in the literature of (adaptive) robust control is that the strong robustness is obtained under no high-gain condition and hence there is no phenomenon for the possibility of saturating the input channel. Furthermore, the present adaptive controller remains to have asymptotic tracking capability in an ideal case, which is hard to obtain by a conventional (adaptive) robust controller under practical design